Fix/170 first tab should be content

[markconroy]

Closes #170

[tonypaulbarker]

It looks as though the behat test is checking the label.

1. Drupal\Tests\localgov_subsites\Functional\SubsitePagesTest::testSubsiteFields
   Behat\Mink\Exception\ResponseTextException: The text "Description" was not found anywhere in the text of the current page.

Worth mentioning that there is a 'Page Content' label on the Page Builder tab for these content types. I'm on the fence about the consistent first item and the two content labels.

[willguv]

@tonypaulbarker I think don't make the change for Subsite overview as content is added elsewhere. Thanks for spotting this

[tonypaulbarker]

At merge Tuesday we decided to close this as the content is on the page builder tab so we'll keep the original label.